Since a developing device using a one-component developer containing no carrier (hereinafter referred to as the "toner") as developer has a simple structure and is producible at a low cost, it has advantages of reducing the size and limiting an increase in the cost. In particular, since a developing device using a non-magnetic one-component toner which does not use a magnetic toner does not require a magnet roller, it has an advantage of achieving a small, clear, inexpensive developing device.
In the developing device using the non-magnetic one-component toner, a blade as a toner layer thickness regulating member is provided so as to form a toner layer of a predetermined thickness on a development roller which is rotated to develop an electrostatic latent image on a photoreceptor.
Regarding the blade, various techniques have been conventionally disclosed.
For instance, Japanese publication of examined patent application No. (Tokukosho) 63-16736 (published on Apr. 11, 1988) discloses a blade. According to the technique disclosed in this publication, a surface of a plate-like member is brought into contact with a development roller, and the toner is regulated by pressing the plane or body of the blade against the development roller.
Meanwhile, Japanese publication of examined patent applications Nos. (Tokukosho) 51-36070 (published on Oct. 6, 1976) and (Tokukosho) 60-15068 (published on Apr. 17, 1985) disclose a blade whose tip or edge is brought into contact with a development roller.
By the way, among these known blades, a blade whose plane or body is brought into contact with a development roller has the following problems. Specifically, when toner which shows excellent fusion of the toner and excellent flowability for the supply of the toner to the development roller is used, it is necessary to increase the pressing force for pressing the blade against the development roller in order to ensure a desired toner deposit optimum for development. As a result, the driving torque of the development roller is increased.
In contrast, in the case of the blade whose tip or edge is brought into contact with the development roller, the toner layer becomes very thin. Therefore, a sufficient toner deposit for development can not be obtained in a stable manner.
On the other hand, there has been a compromising proposal between these blades to obtain a desired toner deposit under an intermediate condition between a condition that the plane or body of the blade is brought into contact with the development roller and a condition that the tip or edge of the blade is brought into contact with the development by adjusting the setting position of the blade. However, this proposal suffers from such a drawback that there is an extremely small margin for error in setting the position of the blade.
As means for overcoming the above-mentioned drawbacks, a blade whose tip has an L-shaped cross section is disclosed in Japanese publication of examined patent application No. (Tokukohei) 6-52449 (published on Jul. 6, 1994), U.S. Pat. Nos. 5,338,895, 5,373,353, 5,587,551, etc.
Moreover, a blade which is inclined at a small angle instead of forming its tip to have an L-shaped cross section is disclosed in U.S. Pat. No. 5,552,867, Japanese publication of unexamined patent applications Nos. (Tokukaihei) 7-64391 (published on Mar. 10, 1995) and (Tokukaihei) 7-239611 (published on Sep. 12, 1995). With such a blade, it is possible to achieve a desired toner deposit and increase the margin for error in the setting.
However, when the above-mentioned conventional one-component developer device uses a method for bringing into contact with the development roller a bent section of a blade having an L-shaped cross section as disclosed in Japanese publication of examined patent application No. (Tokukohei) 6-52449, U.S. Pat. Nos. 5,338,895, 5,373,353, 5,587,551, etc., the following problems arise. Specifically, when forming the inclined section by bending the blade to have a substantially L-shaped cross section as described above, distortion occurs due to the residual stress after bending. It is therefore difficult to ensure the straightness of the bent section of the blade, which comes into contact with the development roller. Thus, there is a problem that the toner layer has unevenness corresponding to the unevenness of the surface of the blade.
Incidentally, the tilt angle of the tip section of the blade disclosed in the above-mentioned U.S. Pat. No. 5,582,867 is between 5.degree. and 15.degree.. Furthermore, it is known from the contents of Japanese publication of unexamined patent applications Nos. (Tokukaihei) 7-64391 and (Tokukaihei) 7-239611 that the angles described in these documents are also limited substantially to the above range.
However, according to the study of the present inventors, the toner deposit is decreased and the image density is lowered under the above-mentioned conditions due to the deterioration of toner with time, such as deterioration of the flowability, caused by the separation of an additive from the surface of the toner.
Moreover, as disclosed in the above publications, since the toner deposit varies depending on the length of the inclined tip section, it is necessary to strictly control the dimensional tolerance of the length of the inclined tip section. Thus, it is difficult to fabricate the blade.
Furthermore, as described in the above-mentioned conventional example, when the blade is mechanically bent for the fabrication of the inclined section, the straightness of the blade deteriorates due to the residual stress after bending. Thus, there is a problem that a uniform toner layer can not be formed along an axis direction of the development roller.
Besides, when a rolled material is used as a material for the blade, a large distortion occurs due to the residual stress after rolling. As a result, like the above example, the straightness of the blade deteriorates, and a uniform toner layer can not be formed along an axis direction of the development roller.